Heat transfer system using solar energy

ABSTRACT

A system for heating a fluid conveyed or contained in a pipe or other process equipment by solar energy is disclosed. The system includes passive and active control methods to control the temperature of the fluid within a selected temperature range. The passive methods use the natural properties of selected materials for the system and the geometry and the orientation of the materials to control the temperature range. The active methods uses one or more than one control mechanism for changing the ratio of energy gain and heat loss at any point in time during a day and between days and across seasons, with these mechanisms including mechanisms to control energy transfer in and heat transfer out of the fluid.

The present invention relates to a system for heating a fluid conveyed or contained in process equipment by solar energy.

The term “process equipment” as described herein is understood to mean pipes, tanks, pumps and the like that are used in industry to convey or contain fluids.

The invention is concerned principally, although by no means exclusively, with fluids which must be maintained at temperatures in excess of ambient temperature. Such fluids include fuel oil, palm oil, and crude oil.

Conventional systems for heating fluids in such process equipment are based on electric heating and steam heating. It is important that the heating equipment be of a high reliability since failure of the heating equipment would change the effectiveness of the process equipment. As a consequence, invariably the initial purchase price and on-going maintenance costs of the conventional systems are high.

International publIcation WO 90/04143 in the name of John Beavis Lasich discloses a system for heating a fluid conveyed or contained in process equipment by solar energy. The system is described particularly in the context of heating pipes conveying fluids, such as hydrocarbon products, where it is desirable to maintain the temperatures of fluids above minimum temperatures and below maximum temperatures for operational and product quality reasons.

The applicant has made a series of improvements to the basic technology described in the International publication.

In general terms, a system for heating a fluid conveyed or contained in a pipe or other process equipment in accordance with the present invention include

-   -   (a) an aperture for allowing energy transfer from solar         radiation to the fluid, the aperture including a layer of a         first material on at least a part of the pipe or other process         equipment, with the layer of the first material being (i)         transparent to solar radiation so that solar radiation can pass         through the first material with minimal energy loss and heat the         fluid during periods when solar radiation is incident on the         pipe or other process equipment and (ii) a thermal insulator to         minimise heat loss from the fluid via the first material at all         times, and         -   (b) a layer of a second material on at least a part of the             pipe or other process equipment that is not transparent to             solar radiation and is a thermal insulator to minimise heat             loss from the fluid via the second material at all times.

The relative amounts of the first and second materials that are required in any given situation depend on a range of factors, including but not limited to, the climate in the area in which the pipe (or other process equipment) is located, the orientation of the pipe or other process equipment to the Sun and therefore the extent to which solar radiation is incident on the pipe or other process equipment during the course of daylight hours and across seasons, the properties of the fluid contained in the pipe or other process equipment, the target temperature for the fluid, the size of the pipe or the other process equipment (typically, the pipe and vessel diameters for many applications are at least 200 mm), the physical structure and resultant characteristics of the layers of the first and second materials (for example, the extent to which the layer of the first material allows transmission of solar radiation at different times of a day), and the properties of the first and second materials.

The above reference to “properties of the first and second materials” is concerned particularly with the transparency of the materials to solar radiation and the thermal insulation properties of the materials.

A relevant factor in relation to the issue of a target temperature for the fluid is the need to design the system so that the amount of heat transferred to the fluid in the pipe or other process equipment is sufficient to achieve and maintain the fluid target temperature during the course of each 24 hour period and to take into account temperature variations during the course of each 24 hour period that may cool the fluid below the target temperature or overheat the fluid. It is also relevant to consider these daily temperature variations in the context of the extent to which there may be successive days of low solar radiation and the impact on maintaining fluid temperature. This requires a wider view on seasonal changes. This factor requires a more complex consideration than designing the system simply so that the total amount of heat transferred to the fluid in the pipe or other process equipment during a 24 hour period is at least the same as the total amount of heat lost from the fluid during the 24 hour period.

As is indicated above, the term “transparent to solar radiation” in the context of the first material means that solar radiation can pass through the material with minimal loss of energy. Typically, the mechanism for energy transfer through the material is radiation as opposed to convection or conduction.

The terms “minimal energy loss” and “minimal loss of energy” are understood herein to mean that no more than 25%, typically no more than 15%, more typically no more than 10%, of the energy of the solar radiation is lost, for example as heat, as the solar radition passes through the first material.

The term “minimise heat loss” in the context of the first and second materials is understood herein to mean that there is no more than 25%, typically no more than 15%, heat loss from the fluid compared to a pipe of other process equipment that is not covered by the first and the second materials.

The term “thermal insulator” in the context of the first and second materials is understood herein to mean a material that has a high resistance to transferring energy in the form of heat through the material. The mechanisms for heat transfer may be any one or more of conduction, convection and radiation, and generally is a combination of these mechanisms.

One example of a thermal insulator that is suitable for use for the layers of the first and/or the second materials is a material marketed under the trade mark Aerogel. Aerogel™ material is one example of many possible suitable bulk insulation materials for the first and/or the second materials.

The improvements made by the applicant to the basic technology described in the International publication are discussed below under the headings “Enhancing Temperature Increase”, “Controlling Temperature”, and “Manufacture of System”.

1. Enhancing Temperature Increase

It is important to maximise the ratio of (a) heat gain in the fluid in the pipe or other process equipment as a result of exposure to solar radiation and (b) heat loss from the fluid as a consequence of heat transfer from the fluid.

The options to increase this ratio fall into two categories, namely (a) maximising solar heat gain and (b) minimising thermal heat loss.

In the case of a pipe or other process equipment, for a given outer surface area for the pipe of other process equipment, the area for solar heat gain may be increased by increasing the thickness of the layer of the first material, i.e. the material that is transparent to solar radiation, on the pipe or other process equipment. More particularly, in the case of a cylindrical pipe that has an aperture defined by sides that extend outwardly, typically radially outwardly, from the pipe, an increase in the thickness of the layer results in an increase in the circumference of the outer surface of the layer and, as a consequence, an increase in the surface area exposed to solar radiation. In effect, increasing the thickness of the layer of the first material increases the aperture size.

In addition, or alternatively, for a given thickness of the layer of the first material, the solar heat gain may be increased by changing the effective aperture size by providing a reflective surface on the sides of the aperture to reflect solar radiation from the reflective surface into the aperture.

In addition, or alternatively, for a given thickness of the layers of the first material, the solar heat gain may be increased by increasing the aperture size by increasing the coverage, i.e. the proportion, of the layer of the first material on the pipe or other process equipment in relation to the coverage, i.e. the proportion, of the layer of the second material on the equipment.

In addition, or alternatively, the solar heat gain may be increased by providing the system with an optical element such as a reflector that increases the amount of solar radiation that is incident on the aperture.

In the case of a pipe or other process equipment, the thermal heat loss may be minimised by selecting materials with high thermal insulation properties for the first and second materials.

In addition, or alternatively, the thermal heat loss may be minimised by providing the aperture with an emissivity control means that reduces the emissivity of the aperture to minimise loss of heat from the pipe or other process equipment by radiation.

For example, the emissivity control means may include a low emissivity coating on the pipe or other process equipment. The coating may be any suitable coating.

In addition, or alternatively, the emissivity control means may include a means that changes the optical characteristics of the aperture to minimise loss of heat from the pipe or other process equipment via the aperture by conduction and/or convection and/or radiation.

For example, the emissivity control means may include an air gap between the section of the pipe or other process equipment and the layer of the first material.

The emissivity control means may also include a material for the first layer that transmits certain wavelengths of solar radiation and prevents or minimises transmission of heat via radiation emitted from the fluid in the pipe or other process equipment. For example, the material for the first layer may be selected to transmit short wavelength radiation through the layer to the pipe of other process equipment and to minimise or prevent transmission of longer wavelength radiation emitted from the pipe or other process equipment.

In addition, or alternatively, the thermal heat loss may be minimised by decreasing the aperture by decreasing the coverage, i.e. the proportion, of the aperture on the pipe or other process equipment in relation to the coverage, i.e. the proportion, of the layer of the second material on the equipment.

In addition, or alternatively, the thermal heat loss may be minimised by locating the aperture in a relatively shielded area, i.e. an area of the pipe or the other process equipment that does not transfer heat to the same extent as other areas of the pipe or other process equipment. Typically, this means that the aperture is positioned in a downwardly-facing section of the pipe of other process equipment. In this position, the aperture and, more particularly the layer of the first material is shielded from direct exposure to solar radiation and therefore there is an issue with respect to heating the fluid in the pipe or other process equipment in the first instance. In order to address this issue, the system may include an optical element such as a reflector that is positioned to receive solar radiation and to reflect the radiation to the aperture for increasing the amount of solar radiation that is incident on the aperture.

2. Controlling Temperature

The applicant has realised that controlling the temperature of the fluid in the pipe or other process equipment to be at a target temperature (or within a selected target temperature range, i.e. within minimum and maximum temperatures), and with minimal variations in temperature during each 24 hour period or longer time period are important considerations in many instances.

For example, in the case of fluids such as crude oil, if the temperature of the crude oil being pumped in a pipe becomes too high, light fractions in the crude oil may volatilise in the pipe and make pumping difficult as a consequence. In addition, the volatilisation of the light fractions may reduce the economic value of the crude oil.

It is important to match heat loss and a target fluid temperature within a pipe or other process equipment. This may involve considering situations where there is a target temperature of say 34° C. inside a pipe and there are temperature variations in a day and across the year ranging from 20-40° C. during sunlight hours. Hence, in this situation, the selection of the design parameters for the system has to take into account specific scenarios including, for example, where there is 34° C. outside the pipe and the requirement for 34° C. inside the pipe versus 40° C. outside the pipe and the requirement for 34° C. inside the pipe versus 20° C. outside the pipe and the requirement for 34° C. inside the pipe.

Depending on the circumstances, the design considerations may be more focussed on providing sufficient heat to fluids during the daylight hours in winter. In other situations, the design considerations may be more focussed on minimising heat transfer to fluids in pipes or other process equipment during the daylight hours in summer.

There are a number of options for controilling fluid temperature in accordance with the present invention.

The aperture may be formed to selectively allow the transmission of solar radiation through the aperture depending on the position of the Sun in relation to the pipe or other process equipment to control the amount of solar radiation that is transmitted to the fluid during different periods of the daylight hours and taking into account seasonal issues, i.e. the different position of the Sun in different seasons.

For example, the aperture may be formed or arranged to selectively control (i.e. minimise in this instance but maximise in other instances) the transmission of solar radiation through the layer of the first material during the middle of a day when there is a high concentration of solar radiation that is incident on the pipe or other process equipment and hence a higher possibility of overheating the fluid than at other parts of the day or when the pipe is already at the target temperature.

In this scenario, the layer of the first material may include a material that includes a bundle of parallel hollow tubes of transparent or partially transparent material or of a material that has reflective walls that are selectively positioned so that the length dimension of the tubes is aligned with the direction of solar radiation during cold periods (which may be a part or parts of a day or across a number of days or seasonal) so that there is minimum restriction to transmission of solar radiation and, as a consequence, the length dimension of the tubes is not aligned with the direction of solar radiation during hot periods (which may be a part or parts of a day or across a number of days or seasonal) so that there is maximum restriction to transmission of solar radiation during this period. The tubes may be any suitable cross-sectional shape including circular, ellipical and rectangular. By way of example, the material may be a material that is marketed under the trade mark Kapipane.

In a more general sense, the alignment of the bundle of tubes may be selected to maximise the acceptance of solar radiation at a time when it is most needed or to minimise the acceptance of solar radiation at a time when it is least desired.

By way of further example, the aperture may include a plurality of louvers that may be fixed or selectively adjustable to control the amount of solar radiation received by the aperture and hence the temperature of the fluid. The louvers may have reflective or opaque walls.

In addition, or alternatively, the system may include an optical element such as a reflector that increases the amount of solar radiation that is incident on a given area of the aperture and can be adjusted to vary the amount of reflected solar radiation that is incident on the aperture during the course of the daylight hours. The reflector or other suitable optical element may be movable or capable of being selectively positioned to maximise solar radiation transmission during times of a day when maximum solar radiation input is required and to minimise solar radiation transmission during times of the day when minimum solar radiation input is required.

There are two issues to consider in relation to the use of optical elements and other options for changing an aperture. One issue is collection of solar radiation and the other issue is transfer of solar radiation to an aperture. One example of collection management is to move a reflective surface in relation to the Sun and an aperture so that the aperture collects more or less solar radiation. The reflective surface may be mounted to the system via a bimetallic material or other suitable means that is responsive to temperature, whereby the reflective surface moves in response to heating or cooling of the bimetallic material to increase or decrease the aperture. One example of transfer management is to vary the reflectivity of the reflective surface to control the amount of solar radiation which is reflected to the fluid.

In addition, or alternatively, the aperture may be formed to be responsive to temperature.

For example, the aperture may be formed so that the thermal insulation properties of the aperture decrease as the temperature increases and vice versa.

By way of further example, the aperture may include a thermochromic layer which reduces the transmission of solar radiation when the temperature of the thermochromic layer reaches a threshold temperature and vice versa.

The thermochromic layer may be formed to be responsive to a selected threshold temperature. Depending on the geographical location of a pipe or other process equipment and the heat requirements for the process equipment, thermochromic materials with different threshold temperatures may be used.

There may be situations in which it is desirable to manage the fluid temperature by controlling the thermal conductivity of the layers of the first and second materials. By way of example, the control may be based on selecting a material that has a strong or controllable positive coefficient of thermal conductivity for heat transfer from the fluid in the pipe or other process equipment. This is a different consideration to controlling energy transfer derived from solar radiation into the fluid. There are situations in which two systems have the same capacity to control such energy transfer into the fluid but have different thermal conductivities and hence different levels of control over the loss of heat from the fluid to the outside. By way of example, the materials may have a threshold temperature where there a significant change in thermal conductivity. In particular, the thermal conductivity may increase significantly if the temperature in the fluid exceeds a particular selected temperature. With this arrangement, there will be an increase in the capability of the system to transfer heat from the fluid to the outside. In some situations, this is a desirable property. Specially, this is a desirable property in situations where it is important to avoid overheating of fluids.

It can be readily appreciated that the aperture may include a combination of options for controlling fluid temperature, with the options being selected from one or more of the above-described options.

By way of example, the aperture may include a combination of (a) one or more than one layer of the first material in the form of a bulk insulation material such as Aerogel™ and (b) one or more than one selective energy transfer layer such as a Kapipane™ layer, louvers, an air gap, and a thermochromic material layer.

The aperture may include materials that have a combination of properties. For example, the aperture may include a bulk insulation material that has a coating of thermochromic material. By way of particular example, the bulk insulation material may be in the form of granules that have a coating of a thermochromic material. Hence, when the fluid temperature exceeds a threshold temperature, the thermochromic material activates and restricts light transfer to the fluid.

3. Manufacture of System

The present invention also provides a method of manufacturing a pipe that comprises a system for heating a fluid that, in use, is conveyed or contained in the pipe positioned on an outside surface of the pipe, with the system comprising an aperture for allowing energy transfer from solar radiation to the fluid, the aperture including a layer of a first material that is transparent to solar radiation and a thermal insulator on at least a part of the circumference of the pipe, and the system further comprising a layer of a second material that is not transparent to solar radiation and is a thermal insulator on at least another part of the circumference of the pipe, and with the method comprising co-extruding the first and the second layers on the pipe.

The present invention also provides a method of manufacturing a pipe or other process equipment that comprises a system for heating a fluid that, in use, is conveyed or contained in the pipe or other process equipment positioned on an outside surface of the pipe or other process equipment, with the system comprising an aperture for allowing energy transfer from solar radiation to the fluid, the aperture including a layer of a first material that is transparent to solar radiation and a thermal insulator on at least a part of the outer surface of the pipe or other process equipment, and the system further comprising a layer of a second material that is not transparent to solar radiation and is a thermal insulator on at least another part of the outer surface of the pipe or other process equipment, and with the method comprising positioning the layer of the first material on the pipe, forming a mould that defines an outer wall of the layer of the second material, and injecting the second material to fill the mould.

The outer mould may be made from a black polycarbonate or black polypropylene or other suitable material and the injected material may be polyurethane or other suitable insulation material.

The present invention also provides a method of manufacturing a pipe or other process equipment that comprises a system for heating a fluid that, in use, conveyed or contained in the pipe or other process equipment positioned on an outer surface of the pipe or other process equipment, with the system comprising an aperture for allowing energy transfer from solar radiation to the fluid, the aperture including a layer of a first material that is transparent to solar radiation and a thermal insulator on at least a part of the outer surface of the pipe, and the system further comprising a layer of a second material that is not transparent to solar radiation and is a thermal insulator on at least another part of the outer surface of the pipe or other process equipment, and with the method comprising positioning an outer casing around the pipe or other process equipment, with the casing having a section that is transparent to solar radiation that corresponds to the required location of the aperture, locating the layer of the first material between the pipe or other process equipment and the casing, and injecting the second material to fill the remaining volume defined by the outer casing and the pipe or other process equipment.

The above-described methods make it possible to optimise materials selection in a straightforward manufacturing process and provide considerable scope to customise systems within basic mass production methodology

The present invention also provides a pipe or other process equipment and the above-described system for heating a fluid conveyed or contained in the pipe or other process equipment.

The present invention also provides a preformed panel that is suitable for use as a part of a system for heating a fluid that, in use, is conveyed or contained in a pipe or other process equipment, with the panel conforming to the shape of a section of the pipe or other process equipment, and the panel including an aperture for allowing transfer of energy of solar radiation through the fluid, the aperture including a layer of a first material, with the layer of the first material being (i) transparent to solar radiation so that solar radiation can pass through the first material with minimal energy loss and (ii) a thermal insulator to minimise heat loss via the first material.

The panel may also include a layer of a second material that is not transparent to solar radiation and is a thermal insulator.

The panel may also include any one or more of the above-described combinations of (a) one or more than one layer of the first material in the form of a bulk insulation material such as Aerogel™ and (b) one or more than one selective energy transfer layer such as a Kapipane™ layer, louvers, an air gap, and a thermochromic material layer.

The panel may be formed to interfit with one or more other such panels and/or with panels that comprise a layer of the second material only.

The panel may be manufactured by any suitable method.

The present invention is described further by way of example only with reference to the accompanying drawings, of which:

FIG. 1 is a transverse section through an embodiment of a system for heating a fluid of the invention described in International publication WO 90/04143.

FIG. 2 is a graph of the temperature of a fluid in a pipe versus time over a 48 hour period that shows the variation in temperature during that period, with the lower plot relating to a pipe that conveys the fluid at ambient temperature (20° C.) and the upper plot relating to a pipe that conveys the fluid at an aim temperature of 50° C.;

FIG. 3 is a transverse section through one embodiment of a system for heating a fluid in accordance with the present invention;

FIG. 4 is a transverse section through another embodiment of a system in accordance with the present invention;

FIG. 5 is a transverse section through another embodiment of a system in accordance with the present invention;

FIG. 6 is a transverse section through another embodiment of a system in accordance with the present invention;

FIG. 7 is a transverse section through another embodiment of a system in accordance with the present invention;

FIG. 8 is a transverse section through another embodiment of a system in accordance with the present invention;

FIG. 9 is a transverse section through another embodiment of a system in accordance with the present invention;

FIG. 10 is a transverse section through another embodiment of a system in accordance with the present invention;

FIGS. 11 and 12 are transverse sections through another embodiment of a system in accordance with the present invention;

FIG. 13 is a partially cut-away perspective view of the embodiment shown in FIGS. 12 and 13.

FIG. 1 is FIG. 1 of the International publication WO 90/04143.

FIG. 1 shows a pipe 7, a fluid 5 conveyed in the pipe 7, and a system 3 for heating the fluid 5 in the pipe 7 as described in International publication WO 90/04143.

The system is equally applicable to other types of process equipment used in industry to convey or contain fluids, such as tanks and valves.

The system 3 comprises an aperture generally identified by the numeral 15 for allowing energy transfer from solar radiation to the fluid 5. The aperture 15 comprises a layer 9 of first material on an upper part of the pipe 7 that is (i) transparent to solar radiation so that the solar radiation can heat the fluid during periods when solar radiation is incident on the pipe and (ii) a thermal insulator to minimise heat loss from the fluid via the first material at all times.

The system 3 also comprises a layer 11 of a second material on the remainder of the pipe 7 that is not transparent to solar radiation and is a thermal insulator to minimise heat loss from the fluid via the second material at all times.

The system 3 further comprises a transparent weather shield 10, of U.V. stabilised polycarbonate, which covers the outer surface of the layer of transparent insulation 9.

With such an arrangement the aperture 15 defined by the layer 9 of the first material defines a “window” through which solar radiation can pass to contact the exposed upper section 13 of the pipe 7 thereby to heat the fluid 5 in the pipe 7. The surface area of the aperture is substantially larger than that of the exposed upper section 13 of the pipe 7, and thus the layer 9 of the first material concentrates to a certain extent the amount of energy received by the exposed upper section 13 of the pipe 7 such that the amount of the energy is greater than that received had there been no layer 9 of the first material

The size, of the aperture can be varied depending on a number of factors which include, the nature of the fluid to be heated, the size of the pipe 7, the required temperature of the fluid 5, the temperature conditions in the environment in which the pipe 7 is located (including the seasonal variation of the temperature conditions), and the type and thickness of the layer 11 of the second material.

The principal function of the layer 11 of the second material is to minimize the heat loss from the fluid, particularly at night. Where there is a low level of solar radiation and/or a necessity to heat the fluid in the pipe 7 to relatively high temperatures, the layer 11 of the second material may be replaced altogether with the layer 9 of the first material. In this regard, the layer 9 of the first material will limit the heat loss from the pipe 7, and thus in certain circumstances where the heat loss through the night is not a critical factor such an arrangement may be acceptable.

The system of the present invention, like that described in the International publication, is concerned with maintaining fluid temperatures in pipes and other process equipment above minimum temperatures and below maximum temperatures for operational and product quality reasons.

As is indicated above, the design of such systems has to take into account a range of factors including the outside atmosphere temperature variations during a day and between days and across seasons.

FIG. 2 illustrates typical temperature variations through a day. The lower plot relates to a pipe that conveys a fluid at ambient temperature (20° C.). The upper plot relates to a fluid that has a preferred operating temperature of 50° C. and a minimum flow temperature of 44° C. and a maximum exposure temperature

Where a fluid must be above ambient temperature, a desirable objective is to use solar radiation to provide heat to the fluid to maintain the fluid temperature between the minimum flow temperature and the maximum exposure temperature. The applicant has realised that it is important to maintain control over the fluid temperature to avoid temperatures below and above the selected limits of the range.

The present invention includes passive and active control methods to achieve this objective. The passive methods use the natural properties of selected materials for the system and the geometry and the orientation of the materials to control the temperature range. The active methods uses one or more than one temperature control mechanism for changing the ratio of energy gain and heat loss at any point in time during a day and between days and across seasons, with these mechanisms including mechanisms to control energy transfer in and heat transfer out of the fluid.

In the following description of embodiments of the system of the invention shown in FIGS. 3 to 13, the same numerals used in FIG. 1 are used to describe the same features in the embodiments.

The systems 3 shown in FIGS. 3 and 4 include (a) a layer 9 of the first material formed from a suitable bulk thermal insulation material that allows transmission of solar radiation therethrough to heat the fluid 5 in the pipe 7 and (b) a layer of a second material formed from a suitable bulk thermal insulation material. One suitable material for the first material 9 is Aerogel™ material.

One difference between the systems 3 shown in FIGS. 3 and 4 is that the layer 9 of the first material is larger in the FIG. 3 embodiment than in the FIG. 4 embodiment. The selection of the size of the aperture 15 in this way is one of a number of options for increasing the solar radiation received by the fluid 5 in the pipe 7.

In any given situation, the selection of the circumferential extent (and the thickness) of the layers 9, 11 will be determined having regard to factors such as the temperature variations in the geographical location and the required target temperature of the fluid 5.

Another difference between the systems 3 shown in FIGS. 3 and 4 is that the FIG. 4 system includes reflective surfaces 33 at the interfaces of the aperture 15 and the layer 11 of the second material to reflect solar radiation into the aperture 15. The reflective surfaces 33 are another option to increase the solar radiation received by the fluid 5 in the pipe 7. The reflective surfaces 33 may be of any suitable type.

Each system 3 shown in FIGS. 3 and 4 also includes a reflector 17 positioned to reflect solar radiation into the aperture 15. The reflectors 17 are another option to increase the solar radiation received by the fluid 5 in the pipe 7. The reflectors 17 may be of any suitable type. Typically, the reflectors 17 will be positioned at spaced intervals along the length of the pipe 7, with the spacings determined having regard to factors such as the temperature variations in the geographical location and the required target temperature of the fluid 5.

The system 3 shown in FIG. 5 is conceptually the same as the FIGS. 3 and 4 systems 3. The FIG. 5 embodiment includes a pair of reflectors 17 to further increase the solar radiation received by the fluid 5 in the pipe 7 compared to the FIGS. 3 and 4 systems 3.

The FIG. 6 system is an example of a system 3 that is constructed to shield the aperture 15 to minimise heat loss from the fluid 5 by positioning the aperture in an area of the pipe 7 that does not transfer heat to the same extent as other areas of the pipe 7. Typically, this means that the aperture 15 is positioned in a downwardly-facing section of the pipe 7. In this position, the aperture 15 and, more particularly the layer 9 of the first material is shielded from direct exposure to solar radiation and therefore there is an issue with respect to heating the fluid in the pipe 7 in the first instance. In order to address this issue, the system 3 includes a reflector 17 that is positioned to receive solar radiation and to reflect the radiation to the aperture 15 for increasing the amount of solar radiation that is incident on the aperture

The system 3 shown in FIG. 7 is an extension of the system 3 shown in FIG. 6. In the FIG. 7 system 3 the reflector 17 is mounted to the layer 11 of the second material (or otherwise mounted) via a bimetallic strip (or other member) that is responsive to temperature and moves in response to temperature and repositions the reflector to increase or decrease the amount of solar radiation that is reflected onto the aperture 15. This temperature responsive feature controls the amount of solar radiation that is received by the aperture 15. There may be situations in which it is important to decrease the amount of solar radiation received by the aperture 15 as the outside temperature increases. Similarly, there may be situations in which it is important to increase the amount of solar radiation received by the aperture 15 as the outside temperature decreases.

The system 3 shown in FIG. 8 includes an air gap 21 between the layer 9 of the first material and the pipe 7 as an example of an option to control the loss of heat from the fluid 5.

The system 3 shown in FIG. 9 includes a layer of a thermochromic material or a set of louvers 23 on the outside of the layer 9 of the first material. The purpose of the thermochromic material/louvers 23 is to selectively allow the transmission of solar radiation through the aperture 15 depending on the position of the Sun in relation to the pipe 7 to control the amount of solar radiation that is transmitted to the fluid 5 during different periods of the daylight hours and between days and taking into account seasonal issues, i.e. the different position of the Sun in different seasons. The thermochromic material may be any suitable material. The louvers may be of any suitable construction and orientation. The louvers may be positioned at spaced intervals along the length of the pipe 7. The louvers may be aligned parallel or transverse to the pipe direction. The louvers may be adjustable to change the angle of the louvers to vary the amount of solar radiation that passes through the aperture 15.

In the system 3 shown in FIG. 10 the thermochromic material/louvers 23 are positioned between the pipe 7 and the layer 9 of the first material.

The thermochromic material and louvers described in relation to FIGS. 9 and 10 are not the only options for achieving temperature control of the fluid 5 in the pipe 7. One of a number of other options is shown in FIGS. 11 to 13. With reference to these Figures, the layer 9 of the first material is formed from a material that comprises a bundle of parallel hollow tubes 25 of transparent or partially transparent material or of a material that has reflective walls that are selectively positioned so that the length dimension of the tubes 25 is aligned with the direction of solar radiation during cold periods (which may be a part or parts of a day or across a number of days or seasonal) so that there is minimum restriction to transmission of solar radiation. As a consequence, the length dimension of the tubes 25 is not aligned with the direction of solar radiation hot periods (which may be a part or parts of a day or across a number of days or seasonal) so that there is maximum restriction to transmission of solar radiation during this period. This is illustrated by the arrows in FIGS. 11 and 12. The tubes 25 may be any suitable cross-sectional shape including circular, ellipical and rectangular. By way of example, the material may be a material that is marketed under the trade mark Kapipane.

Many modifications may be made to the present invention described with reference to the drawings without departing from the spirit and scope of the present invention.

By way of example, whilst the layer 9 of the first material and the layer 11 of the second material are each described and shown in the Figures as being single layers, the present invention is not so limited and each layer may comprise multiple layers, for example with different properties.

By way of further example, whilst the embodiments shown in the Figures include some combinations of different options for maximising the ratio of energy gain and heat loss from fluid in pipes (or other process equipment) and options for controlling temperature in the fluid, the present invention is not so limited and extends to a far wide range of options. More particularly, in general terms, the present invention provides considerable flexibility in tailoring systems for heating fluids conveyed or contained in pipes or other process equipment. 

1. A system for heating a fluid conveyed or contained in a pipe or other process equipment by solar energy includes: (a) an aperture for allowing energy transfer from solar radiation to the fluid, the aperture including a layer of a first material on at least a part of the pipe or other process equipment, with the layer of the first material being (i) transparent to solar radiation so that solar radiation can pass through the first material with minimal energy loss and heat the fluid during periods when solar radiation is incident on the pipe or other process equipment and (ii) a thermal insulator to minimise heat loss from the fluid via the first material at all times, and (b) a layer of a second material on at least a part of the pipe or other process equipment that is not transparent to solar radiation and is a thermal insulator to minimise heat loss from the fluid via the second material at all times.
 2. The system defined in claim I wherein, in a case of process equipment in the form of a cylindrical pipe that has an aperture defined by lengthwise extending sides that extend outwardly, typically radially outwardly, from the pipe, the sides include a reflective surface on the sides of the aperture to reflect solar radiation from the reflective surface into the aperture to increase the heat gain in the fluid in the pipe.
 3. The system defined in claim 1 includes an optical element such as a reflector that increases the amount of solar radiation that is incident on the aperture to increase the heat gain in the fluid in the pipe or other process equipment.
 4. The system defined in claim 1 wherein the aperture includes an emissivity control means that reduces the emissivity of the aperture to minimise loss of heat from the pipe of other process equipment by radiation.
 5. The system defined in claim 6 wherein the emissivity control means includes a low emissivity coating on the pipe of other process equipment.
 6. The system defined in claim 6 wherein the emissivity control means includes a means that changes the optical characteristics of the aperture to minimise loss of heat from the pipe or other process equipment via the aperture by conduction and/or convection and/or radiation.
 7. The system defined in claim 6 wherein the emissivity control means includes an air gap between the section of the pipe or other process equipment and the layer of the first material.
 8. The system defined in claim 6 wherein the emissivity control means includes a material for the first layer that transmits certain wavelengths of solar radiation and prevents or minimises transmission of heat via radiation emitted from the fluid in the process equipment.
 9. The system defined in claim 10 wherein the material for the first layer is selected to transmit short wavelength radiation through the layer to the pipe of other process equipment and to minimise or prevent transmission of longer wavelength radiation emitted from the pipe or other process equipment.
 10. The system defined in claim 1 includes locating the aperture in a relatively shielded area, i.e. an area of the process equipment that does not transfer heat to the same extent as other areas of the pipe or other process equipment to minimise heat loss from the pipe or other process equipment.
 11. The system defined in claim 10 wherein the aperture is positioned in a downwardly-facing section of the pipe of other process equipment so that the layer of the first material is shielded from direct exposure to solar radiation.
 12. The system defined in claim 11 includes an optical element such as a reflector for increasing the amount of solar radiation that is incident on the aperture.
 13. The system defined in claim 1 includes means for controlling the temperature of the fluid in the pipe or other process equipment to be at a target temperature or within a selected target temperature rang; and with minimal variations in temperature, during each 24 hour period.
 14. The system defined in claim 13 wherein the aperture is formed to selectively allow the transmission of solar radiation through the aperture depending on the position of the Sun in relation to the pipe or other process equipment to control the amount of solar radiation that is transmitted to the fluid during different periods of the daylight hours and taking into account seasonal issues, i.e. the different position of the Sun in different seasons.
 15. The system defined in claim 14 wherein the aperture is formed or arranged to selectively control (i.e. minimise) the transmission of solar radiation through the layer of the first material during the middle of a day when there is a high concentration of solar radiation that is incident on the pipe or other process equipment and hence a higher possibility of overheating the fluid than at other parts of the day or when the pipe is already at the target temperature.
 16. The system defined in claim 14 wherein the layer of the first material includes a material that comprises a bundle of parallel hollow tubes of transparent or partially transparent material or of a material that has reflective walls that are selectively positioned so that the length dimension of the tubes is aligned with the direction of solar radiation during cold periods (which may be a part or parts of a day or across a number of days or seasonal) so that there is minimum restriction to transmission of solar radiation and, as a consequence, the length dimension of the tubes is not aligned with the direction of solar radiation during hot periods (which may be a part or parts of a day or across a number of days or seasonal) so that there is maximum restriction to transmission of solar radiation during this period.
 17. The system defined in claim 14 wherein the aperture includes a plurality of louvers that are fixed or selectively adjustable to control the amount of solar radiation that is transmitted through the aperture.
 18. The system defined in claim 14 includes an optical element such as a reflector that increases the amount of solar radiation that is incident on a given area of the aperture and can be adjusted to vary the amount of reflected solar radiation that is incident on the aperture during the course of the daylight hours.
 19. The system defined in claim 13 wherein the aperture is formed to be responsive to temperature.
 20. The system defined in claim 19 wherein the aperture includes a thermochromic layer which reduces the transmission of solar radiation when the temperature of the thermochromic layer reaches a threshold temperature and vice versa.
 21. A pipe or other process equipment and the system for heating a fluid conveyed or contained in the pipe or other process equipment defined in claim
 1. 